I. Field of the Invention
This invention relates generally to implantable electronic tissue stimulating apparatus of the type including a pulse generator that is coupled through a medical lead to target tissue, and more particularly to the design of electrical contacts used in a header of such a pulse generator to mechanically and electrically couple the pulse generator's input/output pins to a proximal terminal of a medical lead.
II. Discussion of the Prior Art
Over the past 30 years great strides have been made in increasing the functional performance of and decreasing the physical size of implantable medical devices, such as those designed for cardiac rhythm management and neural stimulation. Generally speaking, current state-of-the-art implantable medical tissue stimulating devices incorporate a battery power supply and a microprocessor-based controller that is designed to control a pulse generator, causing it to issue pulses at times determined by the microprocessor-based controller. The pulses are conveyed to target tissue on or in the heart by means of one or more medical leads having sensing/stimulating electrodes at a distal end and the electrodes are connected by lead conductors to electrical contacts on a connector pin located at the proximal end of the lead. The lead connector connects the lead to the pulse generator.
While a variety of lead connectors have been devised, a major improvement in lead connectors has been the low profile, in-line bipolar design. An in-line connector places both electrical terminals on a single lead pin, with an insulating barrier separating the anode contact from the cathode contact. To facilitate compatibility between pulse generators and leads of differing manufacturers, standards have been developed. More particularly, a collaborative effort between IEC and International Standards Organization has defined the parameters of a low-profile connector referred to as IS-1 for unipolar and bipolar leads and DF-1 for defibrillator leads. Additionally, there is ongoing work to develop AAMI and potentially ISO standards for connectors for tripolar and quadrapolar leads.
As those skilled in the art appreciate, the lead connector must be mechanically and electrically secured to the implantable device in a way that remains secure following implantation, but which can be readily detached if and when it becomes necessary to install a new pulse generator. The Persuitti et al. U.S. Pat. No. 6,044,302 describes a connector port for an implantable pulse generator that can accommodate a plurality of in-line lead terminal pin having multiple contacts. In the '302 patent, a lead port has one or more connector blocks each including a set screw to lock the lead connector in contact with the connector block. The connector blocks are, in turn, connected to a feed-through wire. A single elastomeric seal is provided within the port such that when the connector pin is inserted therethrough, it precludes ingress of body fluids into the bore in the header. It is also known in the art to provide sealing rings on the lead terminal connector itself for creating a fluid impervious seal upon insertion of the lead's terminal into a connector port. In this regard, reference is made to the Hawkins et al. U.S. Pat. No. 6,029,089.
Copending application Ser. No. 10/222,151 filed on Aug. 16, 2002, and entitled “Connector Port Construction Technique for Implantable Medical Device”, now U.S. Pat. No. 7,047,077, which application is assigned to the assignee of the present application, there is described a connector port for an implantable medical device that is capable of accommodating multiple feedthrough wires and lead connector contacts and that is small in size, easy to assembly and which exhibits a low insertion force. The lead connector contacts described in the aforereferenced application (referred to herein as a toroidal spring design) comprise a metal housing having a circular bore formed through the thickness dimension thereof. The wall defining the bore includes an annular recess for containing a canted-coil spring that is formed as a ring. A number of such electrical contacts are concentrically aligned in a molded plastic header with elastomeric seals disposed between each such contact. A feedthrough wire on the pulse generator is then welded to the housing containing the canted-coil spring. Upon insertion of a lead terminal, the spring is spread to receive a terminal contact therein and the coil spring engages the terminal contact at a multiplicity of points around its circumference.
The use of the currently available spring design is not optimal. The toroidal spring “floats” within the bore of the housing comprising the contact and makes connection between the terminal and spring, and in turn, between the spring and contact housing only through physical interference. This can lead to an unnecessarily high resistance connection between the connector contact member and the contacts on the lead's terminal pin. Other spring designs for this application are too large to fit within the required space or also float within their housing.
It is accordingly a principal object of the present invention to provide a small, improved, cost effective connector contact for use in the header of an implantable pulse generator and which provides a more positive connection between a feedthrough wire of the pulse generator and a lead terminal.